Internal Combustion Engine and Method

ABSTRACT

Internal combustion engine and method with compression and expansion chambers of variable volume, a combustion chamber, a variable intake valve for controlling air intake to the compression chamber, a variable outlet valve for controlling communication between the compression chamber and the combustion chamber, means for introducing fuel into the combustion chamber to form a mixture of fuel and air which burns and expands in the combustion chamber, a variable inlet valve for controlling communication between the combustion chamber and the expansion chamber, a variable exhaust valve for controlling exhaust flow from the expansion chamber, means for monitoring temperature and pressure conditions, and a computer responsive to the temperature and pressure conditions for controlling opening and closing of the valves and introduction of fuel into to the combustion chamber to optimize engine efficiency over a wide range of engine load conditions The relative volumes of the compression and expansion chambers and the timing of the valves are such that the pressure in the combustion chamber remains substantially constant throughout the operating cycle of the engine, and exhaust pressures are very close to atmospheric pressure regardless of the load on the engine The engine runs so quietly and burns so cleanly that in some applications it may not require a muffler and/or a catalytic converter.

RELATED APPLICATIONS

Division of Ser. No. 11/372,751, filed Mar. 9, 2006, which claimed thepriority of:

-   -   Provisional Application No. 60/660,045, filed Mar. 9, 2005;    -   Provisional Application No. 60/660,046, filed Mar. 9, 2005,    -   Provisional Application No. 60/660,050, filed Mar. 9, 2005,    -   Provisional Application No. 60/760,478, filed Jan. 20, 2006,    -   Provisional Application No. 60/760,641, filed Jan. 20, 2006,    -   Provisional Application No. 60/760,642, filed Jan. 20, 2006, the        priority of which are claimed.

BACKGROUND OF THE INVENTION

1. Field of Invention

This invention pertains generally to internal combustion engines and,more particularly, to an internal combustion engine and method capableof operating with high efficiency over a wide range of engine speeds andload conditions.

2. Related Art

Heretofore, engines have been designed for specific uses Gasolineengines may, for example, be designed to maximize power or efficiencyAttempts to set the valving, stroke, and fuel delivery at targets thatprovide both power and efficiency are, by design, compromises of bothWhen different load conditions are factored in, the compromises maybecome even greater

With today's engines, there is much concern about pollution and the highcost of fuel To find a solution to these concerns, it is not onlynecessary to develop an engine that is non-polluting, but also one whichis high in fuel efficiency For fuel efficiency, it is desirable toprovide an engine that is not only efficient at one particular load, butrather over a wide range of operating and load conditions.

OBJECTS AND SUMMARY OF THE INVENTION

It is in general an object of the invention to provide a new andimproved internal combustion engine and method.

Another object of the invention is to provide an internal combustionengine and method of the above character which operate efficiently overa wide range of operating and load conditions.

The engine has compression and expansion chambers of variable volume anda combustion chamber between the compression and expansion chambers Avariable outlet valve controls communication between the compressionchamber and the combustion chamber, and a variable inlet valve controlscommunication between the combustion chamber and the expansion chamber Afuel injector or other fuel inlet introduces fuel into the combustionchamber to form a mixture of fuel and air which burns and expands todrive an output member in the expansion chamber Intake and exhaustvalves control the intake of air to the compression chamber and thedischarge of exhaust from the expansion chamber, and in the disclosedembodiments, those valves are also variable.

The engine also has temperature and pressure sensors for monitoringtemperature and pressure conditions in the compression, combustionand/or expansion chambers and a computer responsive to the temperatureand pressure conditions for controlling the opening and closing of thevalves and the introduction of fuel into to the combustion chamber tooptimize engine efficiency over a wide range of engine load conditions

In some embodiments, the relative volumes of the compression andexpansion chambers and the timing of the valves are such that thepressure in the combustion chamber remains substantially constantthroughout the operating cycle of the engine and the exhaust isdischarged at or very close to atmospheric pressure regardless of theload on the engine

In some disclosed embodiments, the compression and expansion chambersare cylinders with reciprocating pistons in them The pistons areconnected to a crankshaft for reciprocating movement between top andbottom dead center positions in the cylinders The combustion chamber isa separate chamber in which the fuel is burned, and there is no burningof fuel either in the compression cylinder or in the expansion cylinderExpansion of the hot gas from the combustion chamber drives the pistonin the expansion cylinder and produces the reciprocating motion of thepistons.

The volumes of the compression and/or expansion cylinders with thepistons at top dead center are very small In one embodiment, the valvesare rotary valves that do not extend into the cylinders and can remainopen without interfering with the pistons as they travel to their topdead center positions close to the head In some embodiments, the pistontravels to within less than 0.150 inch from the head of the cylinder,and in some, the distance is less than 0.015 inches

The opening of the intake valve is delayed until after the piston in thecompression cylinder has passed top dead center to prevent compressedgas from being a blown back out through the intake manifold, which wouldwaste the work done in compressing the air and compromise the efficiencyof the engine. The delay in opening the valve can range from about 2degrees to 45 degrees of crankshaft rotation, depending upon thecompression ratio of the engine and the amount of air to be taken in.

The engine can have a compression ratio in the range of about 6:1 to24:1, and in some embodiments, greater efficiency is provided with acompression ratio in the range of about 10:1 to 18:1 In someembodiments, where the maximum burn temperature is held too less thanabout 1700° K to prevent NO_(X) from forming, greater efficiency isprovided with a compression ratio in the range of about 9:1 to 14:1.

Unlike conventional reciprocating piston engines with combustion in thecylinders, the compression ratio is determined in part by when theoutlet valve opens to release compressed air from the compressioncylinder to the combustion chamber That generally happens when thecompression piston has completed about 90% to 95% of its upward travel,with the point of opening being higher at higher compression ratios As aresult, the minimum volume of the compression cylinder is not limited bythe compression ratio, and the piston can travel to a higher point inthe cylinder than pistons in engines where combustion occurs in thecylinders and the compression ratio is determined by the volume abovethe pistons at the top of their stroke.

The amount of air and fuel provided to the combustion chamber can beadjusted for different load conditions The timing for the inlet valveand exhaust valve can also be adjusted according to the load In someembodiments, the same amount of air is pumped into the compressionchamber at different loads, but the amount of fuel injected and theamount of gas admitted to the expansion chamber are reduced at lowerloads The inlet valve to the expansion chamber is allowed to remain openfor a shorter period of time at lower loads, with the pressure in theexpansion chamber reaching atmospheric pressure before the pistonreaches bottom dead center This results in below atmospheric pressure asthe piston continues its downward cycle, but the opening of the exhaustvalve is delayed past bottom dead center to allow this negative work tobe recovered during the upward cycle of the piston In this way,efficiency is maintained across a wide range of load conditions.

In some embodiments, compression release braking is provided usingeither or both the compression cylinder and expansion cylinder In oneembodiment, compressed air is allowed to escape from the compressioncylinder into the intake manifold to provide compression release brakingwithout requiring an external muffler In another embodiment, compressionrelease braking is provided using both the compression cylinder andexpansion cylinder in a manner that allows air to be compressed in atleast one cylinder on every revolution of the crankshaft.

In some embodiments, the combustion chamber allows fuel to be ignitedand then diluted with additional air to produce a leaner fuel mixtureand reduce the production of CO The combustion chamber also provides arelatively long burn time to reduce the production of CO In someembodiments, the temperature of the combustion chamber is between about1400 and 1700° K, which is hot enough to ensure that all of the burnproducts are oxidized and cool enough to prevent the formation of NO_(X)Consequently, the exhaust from the engine is essentially free of CO andNO_(X) The long burn time is beneficial in preventing unburnedhydrocarbons and soot from being discharged in the exhaust.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a simplified schematic diagram of one embodiment of aninternal combustion engine incorporating the invention.

FIGS. 2A-2E are diagrammatic views illustrating the operation of theembodiment of FIG. 1.

FIG. 3 is a cross-sectional view, somewhat schematic, of an embodimentof a four cylinder, constant pressure, reciprocating piston internalcombustion engine incorporating the invention.

FIGS. 4-7 are flow charts for different phases in the operation of oneembodiment of an engine incorporating the invention.

FIG. 8 is a graphical representation of the relative torque, horsepowerand fuel consumption for one example of an engine incorporating theinvention and representative engines of the prior art operating undercomparable conditions.

FIG. 9 is a fragmentary cross-sectional view of one embodiment of acylinder with a piston having a configuration for maximizing thecompression ratio in an engine with rotary valves in accordance with theinvention.

FIG. 10 is a fragmentary cross-sectional view of another embodiment of acylinder with a piston having a configuration for maximizing thecompression ratio in an engine with rotary valves in accordance with theinvention.

FIG. 11 is a side elevational view of another embodiment of a piston foruse in the embodiment of FIG. 10.

DETAILED DESCRIPTION

In the embodiment illustrated in FIG. 1, the engine has a compressioncylinder 11 and an expansion cylinder 12 which communicate with oppositeends of a combustion chamber 13, with reciprocating pistons 14, 16 inthe two cylinders forming chambers of variable volume The pistons areconnected to a crankshaft 17 by connecting rods 18, 19 for movement inconcert between top dead center (TDC) and bottom dead center (BDC)positions in the cylinders, with each of the pistons making one upstrokeand one downstroke during each revolution of the crankshaft The termsupstroke and downstroke, as used herein, refer to the direction ofpiston movement toward the positions of minimum and maximum cylindervolume, not the physical directions in which the pistons travel.

Compression cylinder 11 receives fresh air through an intake valve 21and communicates with the inlet end of combustion chamber 13 through anoutlet valve 22 Fuel is injected into the combustion chamber through afuel injector 23 or other suitable fuel inlet, where it is mixed withthe air from the compression cylinder The mixture burns and expands inthe combustion chamber, and the expanding gas flows into the expansioncylinder from the outlet end of the combustion chamber through an inletvalve 24 Exhaust gas is discharged from the expansion cylinder throughan exhaust valve 26.

A combustion chamber which is particularly suitable for use in thisembodiment and others is described in detail in Ser. No. 11/372,737,filed Mar. 9, 2006, the disclosure of which is incorporated herein byreference That chamber is elongated and, in some embodiments, foldedback upon itself, with a rough, twisting interior side wall The chamberis a double wall structure which, in one embodiment, has an outer wallof structurally strong material such as steel and/or a compositematerial and a liner of thermally insulative ceramic material, withlong, sharp protrusions that extend inwardly from the side wall and formhot spots which help to provide complete combustion of the fuel mixturethroughout the chamber

The valves are rotary valves or electronic valves which permit a widerange of adjustment in the timing of the valves A rotary valve systemwhich is particularly suitable for use in this embodiment and others isdisclosed in Ser. No. 11/372,978, filed Mar. 9, 2006, the disclosure ofwhich is incorporated herein by reference The opening or closingpositions of the valves can be varied independently of each other, i.e.,the opening positions can be adjusted without affecting the closingpositions, or the closing positions can be adjusted without affectingthe opening positions In addition, the intake, outlet, inlet, andexhaust valves can all be adjusted independently of each other and whilethe engine is running This full adjustability of the valve systempermits continuous matching of engine performance with every combinationof load and speed.

Unlike the poppet valves traditionally used in conventional Otto andDiesel engines, the rotary valves or electronic valves employed in theinvention do not protrude into the cylinders when they are openConsequently, the engine can have nearly perfect volumetric efficiency,with the volume above the pistons being very close to zero both at theend of the compression stroke and at the beginning of the expansionstroke Having the minimum volumes of the cylinders near zero allows forsignificant improvement in the efficiency of the engine.

With the rotary valves, the only limitation to full piston travel is theneed for a small tolerance or clearance to prevent the pistons fromstriking the head due to thermal expansion or extension at higher enginespeeds This clearance can, for example, be on the order of about 0.010inch to 0.200 inch, and typically does not need to be more than about0.015 inch Hence, the minimum volumes of the cylinders can be muchcloser to zero than they are in other engines Moreover, unlikeconventional reciprocating piston engines where combustion takes placein the same cylinders as compression and expansion, the travel of thepiston toward the top of the cylinder is not limited by the compressionratio In a conventional engine, that ratio is determined by the ratio ofthe cylinder volume at bottom dead center (BDC) to the volume at topdead center (TDC), the need to keep the ratio below a certain level toavoid predetonation limits how close the pistons can come to thecylinder heads In the engine of the invention, where the compressionratio is determined primarily by the timing of the valves and combustionoccurs outside the compression cylinder, the compression ratio does notlimit the travel of the pistons, and the compression piston can travelalmost completely to the head because the outlet valve is opened todischarge the compressed air to the combustion chamber once the correctpressure has been achieved.

Although a rotary valve has the ability to open when the piston is attop dead center (TDC), that is generally not the most desirable way tooperate the intake valves since it can result in compressed gases beingblown out through the intake manifold Opening the intake valve at topdead center would allow compressed air to escape, thereby wasting thework done in compressing it and compromising the efficiency of theengine.

Instead, it is preferable to retard the opening of the intake valveuntil the air in the cylinder has expanded enough to be at or nearatmospheric pressure In this way, the work done to compress the gas isrecovered as the gas pushes against the piston during the initialportion of its downstroke

For example, an engine with a 12.5:1 compression ratio and a 3.76 inchstroke may have a 0.015 inch clearance between the crown of the pistonand the cylinder head If the intake valve were opened at TDC, gas at apressure of 504 PSI would escape and be wasted If, however, the openingof the intake valve is delayed until the piston has moved down to thepoint where the gas has expanded to 12.5 times the volume at TDC, thenthe pressure of the gas above the piston would be at or nearatmospheric, no gas would be lost out the intake valve, and the enginewould still have the same amount of air in the cylinder at BDC even withthe delayed opening of the intake valve.

In the foregoing example, the volume of the gas has expanded to 12.5times the TDC volume when the piston has traveled 11.5×0.015 inch, or0.173 inch, which is 4.6 percent of the 3.76 inch stroke and correspondsto 21.5 degrees of crankshaft rotation With this delayed opening, theslotted openings in the intake valves can be substantially narrower,with the leading edges of the openings being moved back In otherembodiments, the intake valve may open when the compression piston hastraveled past top dead center by a distance on the order of about 2degrees to 45 degrees of crankshaft rotation.

The engine runs because the product of the volume and the pressure ofthe gas sent to the expansion cylinder is greater than the product ofthe pressure and the volume of the air delivered to the combustionchamber from the compression cylinder Ignoring losses, the gas enteringthe expansion cylinder is at the same pressure as the air leaving thecompression cylinder, but at a greater volume by an amount proportionalto the rise in temperature in the combustion chamber That rise isproportional to the amount of fuel injected into the combustion chamber.

The burning of fuel in the engine can easily result in a volumetricexpansion of 2:1, which suggests that the expansion piston should havetwice the area or twice the stroke of the compression piston While thatwould work well at full load, it would not be as efficient when theengine is operating at less than full load and the burn temperature isless than its maximum value Efficiency would be compromised most of thetime since engines are rarely operated at 100% of their maximum loadcapability In the invention, the sizes of the two pistons can be madeequal, as can their strokes, which maintains good mechanical balance,and the amount of air intake can be varied to match the specific needsof the engine under different operating conditions. Thus, for example,with the conditions stated above (equal numbers of compression andexpansion cylinders, pistons of equal size and stroke, and a maximumexpansion ratio of 2:1 at full load), the air intake to the compressoris limited to about 50% If the expansion ratio at full load is otherthan 2:1, then the amount of air intake can be adjusted accordingly,e.g. 40% for a ratio of 2.5:1 For lesser loads and lower power output,the temperature in the combustion chamber and the amount of expansion ofthe gas are reduced.

The engine is not, however, limited to having equal numbers ofcompression and expansion cylinders and pistons of equal size andstroke. It can have any combination of cylinders and piston sizes andstrokes desired and, by adjustment of the air intake and other valves,still maintain optimum efficiency throughout its operating range Theengine can also have more than one combustion chamber between thecompression and expansion cylinders, if desired.

The engine can have virtually any compression ratio because, unlike anOtto cycle engine, there is no fuel to predetonate in the cylinder doingthe compression, which would limit the compression ratio to about 10:1,and unlike a typical Diesel engine, the compression ratio does not haveto be higher than about 18:1 in order to generate enough heat to ensuredetonation The engine can operate with a compression ratio anywhere inthe range of about 6:1 to 24:1, but has the greatest efficiently with aratio of about 10:1 to 18:1, although to prevent NO_(X) from forming,the maximum temperature should be held to about 1700° K-1800° K Underthose conditions, the engine produces maximum fuel efficiency with acompression ratio in the range of about 9:1 to 14:1 The engine can alsooperate at other compression ratios, but possibly not as efficiently Inareas where NO_(X) pollution standards are not as stringent, theefficiency of the engine can be increased by the use of a highercompression ratio.

The compression ratio is controlled by the timing of the intake, outletand inlet valves In typical operation, the outlet valve opens when thepressure above the piston in the compression cylinder equals thepressure in the combustion chamber In an engine having a 9:1 compressionratio in which the compression cylinder is allowed to have a full chargeof air, the outlet valve opens when the piston has completed slightlymore than 90% of its upward travel toward top dead center For othercompression ratios on the order of 10:1 to 18:1, the outlet valve isopened when the compression piston has completed about 90% to 95% of itsupward travel, with the point of opening being higher at highercompression ratios If the compression cylinder is not allowed to have afull charge of air, then the pressure within the cylinder will rise moreslowly, and the outlet valve will open later in the upward strokeRegardless of when the outlet valve is opened, it closes at or near topdead center for maximum efficiency.

The operating cycle of the engine is illustrated in FIGS. 2A-2E In thisparticular embodiment, expansion piston 16 leads compression piston 14by a few degrees, and the opening of inlet valve 24 is timed tocoordinate with the opening of outlet valve 22, which maintains asubstantially constant pressure in combustion chamber 13 That pressureis typically on the order of 200 to 1000 PSI and is dependent upon thecompression ratio Thus, it might, for example, be on the order of 270,370 and 840 PSI for compression ratios of 8:1, 10:1 and 18:1,respectively.

If desired, for maximum engine balance, the two pistons can be timed tobe precisely in phase and to reach top dead center at the same time Thatwill require the inlet and outlet valves to open at slightly differenttimes, which will cause some pressure pulsing However, the pressurepulses are relatively small due to the relatively large volume of thecombustion chamber compared to the volume of air being provided by thecompression chamber Hence, the pulsing will not appreciably affect theefficiency of the engine.

The amount of lead between the expansion and compression pistons dependsupon the compression ratio of the engine With a compression ratio of12.5:1, for example, the expansion piston leads by approximately 15degrees of crankshaft rotation With lower compression ratios, the leadtime is greater, and for higher compression ratios, it is less.

As illustrated in FIG. 2A, at the start of the operating cycle,compression piston 14 is at top dead center, expansion piston 16 is 15degrees past top dead center, and the compression cylinder valves areclosed As the compression piston begins its downward stroke, intakevalve 21 opens as shown in FIG. 2B, and air is drawn into thecompression cylinder Under normal operating conditions, the engineoperates most efficiently when the intake valve is open for an amount oftime such that after the volumetric expansion produced by the burning ofthe fuel in the combustion chamber and the decrease in pressure due toexpansion of the gas in the expansion cylinder, the final pressure atthe end of expansion will be close to atmospheric pressure Keeping theexhaust pressure close to atmospheric pressure reduces the amount ofenergy wasted and provides for maximum efficiency The exhaust valve istypically opened when the pressure is between atmospheric pressure andabout 20% above atmospheric pressure, and in one presently preferredembodiment, it is opened when the pressure is about 2 PSI aboveatmospheric pressure, although that can vary somewhat with RPM asshorter stroke times require more force to get the exhaust out Theexhaust pressure is usually not allowed to go below atmospheric pressuresince that would waste work.

While under most conditions, it is desirable to vary the timing of thevalves for different burn temperatures and loads so that the exhaustpressure remains close to atmospheric pressure, that is not the casewhen it is desired to maximize power output and sacrifice efficiency fora brief period of time, such as when accelerating a vehicle on theentrance ramp to a freeway In an engine having an expansion ratio of2:1, for example, the exhaust pressure at BDC might rise to about 15 PSIover atmospheric pressure at maximum power output, and in a lowercompression engine having an expansion ratio of 3:1, it might rise toabout 30 PSI above atmospheric pressure The ability to increase power inthis manner is useful, and the sacrifice in overall fuel economy isrelatively insignificant since it lasts for only a few seconds It alsopermits the use of a smaller, lighter, less expensive engine with thesame peak power rating as a much larger engine.

The amount of time the intake valve should remain open depends upon theconfiguration of the engine In a four cylinder engine with two expansioncylinders and two compression cylinders of equal bore and stroke, forexample, the engine operates most efficiently under normal conditionswhen the intake valve is open for about 40% of the downward stroke ofthe compression piston In this example, an expansion ratio of 2.5:1would allow the exhaust pressure in the expander to be about equal toatmospheric pressure at when the expansion piston is at BDC and theengine is operating at full load At partial loads, the expansion wouldbe less, the pressure at BDC would be sub-atmospheric, and the exhaustvalve would not open until the piston was on its upstroke and thepressure was back up to or slightly above atmospheric pressure Openingthe exhaust valve on the upstroke has the advantage of recapturing anywork done by the piston on its downstroke when the pressure wassubatmospheric.

With an engine having two compression cylinders and four expansioncylinders where all six cylinders are of equal bore and stroke, thebasic operation of the engine is the same, but the timing of the valvesis different to allow the compression cylinders to take in more airThus, the six cylinder engine operates most efficiently when the intakevalve is open for about 80% of the downward stroke so that with anexpansion of 2.5 in the combustion chamber the pressure in the expanderwill go to atmospheric pressure at BDC when the engine is operating atfull load In the paragraphs which follow, it is assumed that the engineis a four cylinder engine, with cylinders of equal size, and that theintake valve is open for 40% of the downward stroke When the intakevalve closes, the piston continues its downward travel, as illustratedin FIG. 2C.

During the remaining 60% of the downward travel of the compressionpiston, a subatmospheric or negative pressure is developed in thecylinder above the piston, and that requires work However, the pressurein the crankcase below the piston typically remains at or aboveatmospheric pressure, and the work is recovered during the first 60% ofthe upward stroke when the piston is pushed in the upward direction bythe higher pressure below it.

As the compression piston continues its upward travel, the air in thecylinder above it is compressed, and when the pressure in the cylinderreaches the pressure in combustion chamber 13, outlet valve 22 opens asillustrated in FIG. 2D, and the piston pushes the compressed air intothe combustion chamber The outlet valve closes when the compressionpiston is at or near top dead center, as seen in FIG. 2A.

Inlet valve 24 opens at approximately the same time as outlet valve 22,and the expanding gas is transferred from combustion chamber 13 toexpansion cylinder 12, driving expansion piston 16 in a downwarddirection The inlet valve remains open until the volume of gas enteringexpansion cylinder 12 substantially equals the amount of air compressedin compression cylinder 11 times the expansion ratio in the combustionchamber The amount of expansion is dependent upon the amount of fuelwhich is burned, and that, in turn, is determined by the loadencountered by the engine

At full load, for example, with a compression ratio of 9:1, an expansionratio of 2.5:1 can occur in the combustion chamber with a maximum burntemperature of approximately 1700° K In this example, the outlet valvewill be open for approximately the last 10%-12% of the compressionstroke, and the inlet valve will be open for approximately the first25%-30% of the expansion stroke.

At higher compression ratios, the temperature of the compressed gas ishigher, and the pressure in the combustion chamber is higher To get tothe higher compression pressure the outlet valve opens later With thehigher pressure, the inlet vale closes sooner so that when the gas isfully expanded at BDC, it will be at or close to atmospheric pressure.

The expansion ratio which can be used with a given compression ratio islimited by the maximum combustion temperature that can be used withoutcreating pollution With a compression ratio of 13.5:1, for example, acompression temperature of 850° K will rise to 1700° K with an expansionratio of 2:1, whereas with a compression ratio of 10:1 and a maximumburn temperature of 1700° K, an expansion ratio of 2.25 can be used.

The compression piston does work during the compression of the air andwhen it is pushing the compressed air into the combustion chamber Theexpansion piston provides full pressure work output for approximatelythe first 25%-30% of its downward stroke and then continues providingwork output as the pressure in the cylinder drops to approximatelyatmospheric pressure as the piston completes its travel to bottom deadcenter.

When the expansion piston is at or near bottom dead center, exhaustvalve 26 opens, as shown in FIG. 2E, and thereafter the rising expansionpiston pushes the exhaust gases out into the atmosphere Since theexhaust valve opens when the gas in the cylinder is essentially atatmospheric pressure, substantially no energy or work is left in thepressure of the gas, and efficiency is maximized The exhaust valvecloses as the expansion piston approaches top dead center, and the cyclerepeats.

A distinctive feature of the invention is the ability to adjust thevalves to make the pressure in the expansion cylinder close toatmospheric pressure when the exhaust valve is opened with differentloads, thereby maximizing efficiency over a wide range of operatingconditions.

As discussed above, some pressure is required to push the gas out of theexpansion cylinder, and the target pressure at bottom dead center istherefore typically a couple of PSI above atmospheric pressure Thisallows for a shorter expansion stroke than otherwise would be necessary,and engine size can thus be reduced without loss of efficiency.

At lower load conditions, the combustion chamber temperature (burntemperature) is reduced, the expansion of the gas is reduced, and theinlet valve is open for a proportionately shorter period of time Thus,the total work output is reduced with a smaller amount of gas going tothe expansion cylinder For example, at half load, the fuel injected intothe combustion chamber is one-half of the amount injected at full load,and consequently the expansion is only half of what it is with a fullload With the reduced expansion, the inlet valve is open for a smallerportion of the stroke, and in this example, it still opens at or neartop dead center, but it stays open for only about 17.5% of the expansionstroke, rather than about 25%-30% The expansion piston does useful workuntil the gas in the cylinder is expanded and the pressure dropsapproximately to atmospheric pressure, which in this example occurs whenthe piston has traveled about 70% of its downward stroke During the lastpart of the stroke, the expansion piston is working against a partialvacuum and provides negative net work for that part of the stroke Tocompensate for the negative work, the exhaust valve is kept closedduring the first part of the upward stroke, and the lost work isrecovered when the higher pressure below the piston pushes it back upWhen the pressure above the expansion piston approaches atmosphericpressure, the exhaust valve is opened, and the exhaust gases are pushedout of the cylinder by the piston as it completes its upward stroke Inthe example given, the exhaust valve opens when the piston has moved 30%of its upward travel With the exhaust valve being opened at atmosphericpressure, no work is lost, and efficiency is maintained Opening theexhaust valve near atmospheric pressure also avoids loud exhaust noisesand can allow the engine to operate without a muffler Moreover, withfactors such as a longer burn time, no cooling of the combustion chamberwalls, and good temperature control, the exhaust is much cleaner than intypical Otto and Diesel engines, and consequently the engine may notneed a costly catalytic converter either.

The engine is started by introducing air into the compression cylinder,compressing it, pumping the compressed air into the combustion chamber,heating it, and allowing the expanded gas to flow through the inletvalve into the expansion cylinder This is similar to the normaloperation of the engine except that it can be done at very lowpressures, e.g. 2-4 atmospheres The lower pressure can be provided byopening the outlet valve sooner than usual and/or by closing the intakevalve sooner, although this may not be as efficient As air is passedinto the combustion chamber and heated, then expanded in the expansioncylinder, the engine will start to develop a work output which is usedto keep the engine running As the engine starts to run, the inlet valvewill allow less than the normal amount of gas to enter the expansioncylinder, and that causes the pressure in the combustion chamber toincrease until normal operating pressures are obtained This provideseasier starting and the use of a smaller starting motor.

Since the outlet valve of the compression cylinder opens when thepressure in that cylinder reaches the pressure of the gas in thecombustion chamber, by varying the timing of the inlet valve, the outletvalve, the intake valve, or a combination thereof, the pressure in thecombustion chamber can be built up to the normal level necessary for therunning of the engine

When the combustion chamber pressure increases to its normal level, theengine begins normal operation, with the timing of the valves returningto normal running conditions.

Since the engine can maintain the correct or optimum combustion chamberpressure by varying valve timing, the engine can compensate forsituations where normal engine breathing is limited with no loss inperformance Such conditions exist, for example at high altitude, highambient temperature, and low atmospheric pressure as well as at higherengine RPM At high altitude, the air is less dense, the barometricpressure is lower, and the reduction in air pressure would normallycause less air mass to be drawn into the compression cylinder At highambient temperatures, the density of the air is lower than it would beat normal temperatures, and less air mass would likewise be drawn intothe compression cylinder However, since only a portion of the capacityof the compression cylinder is utilized under normal operatingconditions, it is possible to allow the intake valve to be open for alonger period of time when a high ambient temperature or a decrease inbarometric pressure is detected Thus, for example, instead of openingthe intake valve for 40% of the intake stroke, it can be opened for 50%or 60% of the stroke as needed, and this extra capacity will allow agreater volume of air to be drawn into the cylinder and compressed tocompensate for the air being less dense The ability to draw inadditional air can also be used to compensate for breathing losses thatoccur at high RPM The net result in each of these cases is that the samemass of air will be drawn into the engine, the same amount of work willbe required to compress it, and the same work output will be maintainedeven though the density of the air is less at high altitude or hightemperatures and also when breathing is more difficult at high RPM Inthis way, the performance of the engine is maintained over a wide rangeof ambient conditions without any decrease in efficiency or performance.

Under lower load conditions, the same amount of air is still pumped intothe compression cylinder, but less fuel is burned in the combustionchamber Gas expansion is thus reduced, the inlet valve is allowed toremain open for a shorter period of time, and the work output of theexpansion piston is reduced Under these conditions, the pressure in theexpansion cylinder will reach atmospheric pressure before the expansionpiston reaches bottom dead center, and negative work is once again doneHowever, as discussed above, that work is recovered by delaying theopening of the exhaust valve and allowing the higher pressure below thepiston to push it up Once the gas has been compressed back toatmospheric pressure, the exhaust valve is opened to let the gas out.

Thus, the difference in running at partial load is that less fuel isused to heat the mixture in the combustion chamber With the same amountof air, less fuel produces less heating, and less heating produces lessexpansion The reductions in heating and expansion are compensated for byopening the inlet valve for a shorter period of time and by delaying theopening of the exhaust valve In this way, the efficiency of the engineis maintained throughout the load ranges of the engine.

The engine can be turned off or shut down by turning off the fuel supplyor by closing the valves No work output can occur under thoseconditions, and the pressure in the combustion chamber will bemaintained for some period of time The pressure stored in the combustionchamber provides quick and easy restarting of the engine, and it alsoallows the engine to idle at zero RPM, e.g when the vehicle in which itis installed is stopped at a stoplight and valves which can be closedindependently of crankshaft rotation are used

If all of the valves are closed when the expansion piston is at top deadcenter, the pistons will not be under pressure to move, and the pressureand temperature will be maintained in the combustion chamber Since thatchamber is well insulated, it will not lose significant temperature orpressure for several minutes During that time, the engine is notturning, and it is effectively idling at zero RPM

When valves which cannot seal independently of crankshaft rotation areused, zero RPM idling is not possible However, with rotary valves suchas those disclosed in Ser. No. 11/372,978, the engine can idle at speedson the order of 50-300 RPM, which is beneficial in saving fuel, evenwhen the valves are driven from the crankshaft.

When power is once again desired from the engine, the valve sequence canpick up where it left off, and hot pressurized gas from the combustionchamber can once again enter the expansion cylinder and do work If thezero RPM condition is maintained for an extended period of time, theresulting decreases in temperature and pressure are detected by sensorsin the combustion chamber, and the engine is allowed to run for a fewrevolutions in order to maintain a minimum temperature and pressurerelationship in the combustion chamber.

When used in vehicles such as automobiles, the engine will provide somedegree of braking when it is running and the vehicle is coasting In thissituation, the amount of air and fuel going to the combustion chamber isgreatly reduced, and the work output decreases to the point that themoving vehicle is turning the engine The frictional and breathing lossesassociated with turning the engine when there is substantially no energyinput from the limited amount of fuel being burned produce mild enginebraking and a gradual slowing down of the vehicle The amount of brakingcan be increased by opening the exhaust valve when the expansion pistonis at bottom dead center so that the work input during the last portionof the expansion stroke will not be recovered during the exhaust strokeThus, the braking provided by the engine is variable and is controlledby the timing of the valves.

The engine can also provide very effective braking in tractor-trailerrigs and other large trucks, where valve operation is modified toprovide compression release engine braking, one well known form of whichis commonly known as “Jake braking” Compression relief braking is muchmore effective than normal engine braking and can save brake wear andreduce overheating of the brakes, particularly on long downhill gradesand steep declines With the invention, compression release enginebraking can be done in several ways which make it highly flexible andadjustable.

One way to provide compression release engine braking is to close theoutlet and inlet valves and allow air to enter the expansion cylinderthough the exhaust valve during the downward stroke of the expansionpiston The exhaust valve is closed at or near bottom dead center, andthe expansion piston then does work while compressing the air in theexpansion cylinder during the upstroke That work slows down the engineand the vehicle The point at which the exhaust valve opens can beadjusted to provide the amount of braking desired The opening of theexhaust valve releases the pressure and thereby wastes the work whichhas been done The sudden release of the compressed air may produce aconsiderable amount of noise that comes out the exhaust system, whichmay require the use of a muffler that otherwise might not be required innormal operation of the engine.

Compression release engine braking can also be provided with thecompression cylinder by keeping the outlet valve closed, drawing airinto the compression cylinder through the intake valve for all or partof the downstroke of the compression piston, compressing the air duringthe upstroke, and then opening the intake valve to release the pressuretoward the end of the upstroke The work done in compressing the airslows down the engine and the vehicle, and the amount of braking iscontrolled by selection of the point at which the valve opens.

The high pressure air is discharged back into the intake manifold whichcan be closed off from the atmosphere by a one-way flapper valve at theair inlet Since the manifold is larger than the compression cylinder,the pressure of the air is reduced, and the manifold is filled with airat a relatively low pressure During this method of compression releaseengine braking, this same air is moved back and forth between themanifold and the compression cylinder, and no dirt can be sucked backinto the cylinder from the manifold because the intake manifold is veryclean Also, since virtually no air can leak out through the flappervalve to the outside atmosphere, the sound of the sudden pressurerelease is greatly muffled, and an external muffler may not be required.

For maximum compression release engine braking, both the compression andexpansion cylinders can be used This can potentially provide twice thebraking force of conventional compression release engine braking systemsbecause conventional engines typically compress air only once every tworevolutions whereas the invention can compress it on every revolution.

A one-way flapper valve or other suitable valve can be used to shut offair flow in the exhaust system as well as in the intake manifold If thatis done, the external noise produced by the sudden release of pressurein the expansion cylinder will be greatly reduced because the valve willdampen the sound escaping from the engine.

During compression release engine braking, it is possible to allow smallamounts of air and fuel to move through the combustion chamber to allowjust enough burning to take place to maintain the desired temperatureand pressure so that immediate power will be available when it isdesired or needed.

In some embodiments which use rotary valves or other valve systems, itmay not always be possible to move the valves far enough and quicklyenough to fully utilize the compression release braking capability ofthe engine In this case, a small closed chamber and valve can be addedto the compression cylinder The extra chamber can have approximately1/12 to ⅙ of the volume of the compression cylinder, and when the extravalve is open, the compressed air can enter and be stored in the extrachamber during the compression stroke without being over pressurized anddamaging the engine The valve remains open for as long as compressionrelease engine braking is being used.

When the intake valve is opened at top dead center, the compressed airwill escape to the intake manifold, and the engine will be ready for thenext cycle When compression release engine braking is no longer needed,the extra valve is closed, and the other valves resume normal operation.

FIG. 3 illustrates a four cylinder engine incorporating the inventionThis engine has two compression cylinders 31, 32, two expansioncylinders 33, 34 and a combustion chamber 35, with pistons 36, 37 in thecompression cylinders and pistons 38, 39 in the expansion cylinders Thepistons are connected to a crankshaft 40 by connecting rods 41-44 Thecylinders are formed in an engine block 47, and the crankshaft islocated in a crankcase 48 in the lower portion of the block The twocompression pistons are 180 degrees out of phase with each other, as arethe two expansion pistons, so that one piston in each pair is on theupstroke while the other is on the downstroke For good mechanicalbalance in this particular embodiment, the two outer pistons(compression piston 31 and expansion piston 34) are in phase with eachother, as are the two inner pistons (compression piston 32 and expansionpiston 33).

Air is supplied to the compression cylinders through an intake manifold49 and intake valves 51, 52 in cylinder head 53 Those cylinders alsocommunicate with the inlet end of combustion chamber 35 via an outletmanifold 54, with communication between the cylinders and that manifoldbeing controlled by outlet valves 56, 57 The outlet end of combustionchamber 35 communicates with expansion cylinders 33, 34 via an inletmanifold 59, with inlet valves 61, 62 controlling communication betweenthe chamber and those cylinders Exhaust gases are expelled from theexpansion cylinders through an exhaust manifold 63, with communicationbetween the cylinders and the manifold being controlled by exhaustvalves 66, 67.

As in the embodiment of FIG. 1, combustion chamber 35 can, for example,be of the type disclosed in Ser. No. 11/372,737, and valves 51, 52, 56,57, 61, 62, 66 and 67 can be rotary valves of the type disclosed in Ser.No. 11/372,978.

Fuel injectors 68 supply fuel to the combustion chamber, with flowseparators or baffles dividing the region near the fuel inlet intosmaller volumes 69 where the fuel can mix and burn with only a portionof the air introduced into the chamber A safety relief valve 71 providesprotection for the combustion chamber in the event that the pressure inthe chamber should ever rise above a safe level.

In this embodiment, air is drawn into compression cylinders 31, 32during the intake strokes (down) of the pistons in them and iscompressed during the compression strokes (up) of the pistons Sincethose pistons are 180 degrees out of phase with each other, there aretwo intake strokes and two compression strokes for each revolution ofthe crankshaft

The compressed air from cylinders 31, 32 is delivered to combustionchamber 35 during alternate halves of the operating cycle where it ismixed and burned with the fuel from the injectors The expanding gas isdelivered to expansion cylinders 33, 34 during alternate half cycleswhere it drives the pistons down and produces work output.

The timing of the valves relative to the pistons in the embodiment ofFIG. 3 is the same as it is in the embodiment of FIG. 1, the onlydifference being that with two compression cylinders and two expansioncylinders, there are two intake strokes, two compression strokes, twoexpansion strokes, and two exhaust strokes for each operating cycle orrevolution of the crankshaft.

In this particular embodiment, a radiator 73 is shown as being connectedto exhaust manifold 63 for cooling exhaust gases that are low in oxygenand mixing them with fresh air from the intake if the presence of smallamounts of NO_(X) is detected in the exhaust The exhaust system is alsoillustrated as including a muffler 74 in this embodiment In otherembodiments, the radiator and/or the muffler may not be required.

Temperature and pressure sensors monitor conditions throughout theengine and provide that information to a computer 76 which controls thedelivery of fuel to the combustion chamber and the timing of the valvesin accordance with the environmental and load conditions Thus,temperature sensors T1-T4 and pressure sensors P1-P4 monitor temperatureand pressure in the compression and expansion cylinders, and temperaturesensors T5-T10 and pressure sensor P5 monitor temperature and pressurein the combustion chamber.

Temperature sensors T11 and T12 monitor temperature in the engine headand crankcase, temperature sensor T13 monitors temperature in inletmanifold 59, temperature sensor T15 monitors temperature in the intakemanifold, and temperature sensor T14 and pressure sensor P6 monitortemperature in the exhaust manifold An oxygen sensor O1 monitors thelevel of oxygen in the exhaust manifold, and temperature sensors T16,T17 monitor temperature in the cooling system for the engine.

Small chambers A1, A2 provide increased volume above compression pistons37, 37 to prevent over pressure in the cylinders when using compressionrelease engine braking Communication between those chambers and thecylinders is controlled by valves V1, V2.

An additional chamber A3 is also included in the intake manifold toprovide increased volume for receiving the air which is discharged intothat manifold during compression release engine braking A one-wayflapper valve V3, or other suitable valve, controls communicationbetween that chamber and the air inlet, allowing outside air to be drawninto the manifold, but preventing the pressurized air from thecompression cylinders from being discharged to the atmosphere.

The starting routine for an engine incorporating the invention with acompression ratio of 13:1 is illustrated in the flow chart of FIG. 4 Ifthe pressure in the combustion chamber is not more than 450 PSI and theengine sensor is on, the engine is in the startup mode As long as thepressure remains below approximately 476 PSI, the intake, outlet, inletand exhaust valves are set in accordance with the pressure as fuel isinjected into the combustion chamber When the pressure exceedsapproximately 476 PSI, the engine switches to the run mode If the enginesensor is not on or if a timeout occurs before the pressure exceedsapproximately 476 PSI, the engine is shut down.

The run mode is illustrated in the flow chart of FIG. 5 A table fordifferent engine loads is stored in memory, and if the engine isrunning, the fuel delivery is set to be proportional to the load readingas determined by the throttle position Temperature is monitored in thecombustion chamber, and the fuel delivery is adjusted accordingly Theintake, outlet and inlet valves are set for the load conditions, as isthe exhaust valve This process repeats as long as the engine is running.

The routine for adjusting the intake and inlet valves is illustrated inFIG. 6 The pressure in the combustion chamber is monitored to see if itis within tolerances above and below 500 PSI If the pressure is withintolerances, it is checked again after a short time If it is higher thantolerance, the inlet valve(s) is (are) opened slightly, and the pressureis checked again If the pressure is below tolerance, the valve(s) is(are) closed slightly, and the pressure is checked again after a shorttime delay.

As illustrated in FIG. 7, the shutdown routine consists of shutting offthe fuel delivery and setting the valves to their default angles.

With the operation of the valves and the delivery of fuel all undercomputer control, the engine can be programmed or targeted for a widevariety of different applications simply by changing the software Theexhaust valve can, for example, be programmed to open when the pressurein the expansion cylinder is at or near atmospheric pressure for maximumefficiency The temperature and pressure in the combustion chamber aresoftware controlled, as are the amount of air taken into the compressionchamber and the amount of braking provided by the engine By simplechanges in software, it is possible to trade off efficiency, power, andengine braking With such a wide range of control, the engine has aflexibility that other engines do not have

Torque, horsepower, and fuel efficiency curves for exemplary embodimentsof the engine of the invention and conventional Otto, Diesel, and TurboDiesel engines are shown in FIG. 8 These curves are based uponcalculations made for engines of equal air intake (0.95 liter perrevolution), with the engine of the invention having a compression ratioof 13:1, an Otto engine having a compression ratio of 9:1, and Dieseland Turbo Diesel engines having a compression ratio of 19.5:1 As thesecurves show, the engine of the invention produces greater torque and hasa much broader and flatter torque range than the Otto, Diesel and TurboDiesel engines having the same air intake per engine revolution

Curve 77 a represents the calculated torque produced by the engine ofthe invention, curve 78 a represents the calculated torque produced byan Otto engine, and curves 79 a and 80 a represent the calculated torqueproduced by Diesel and Turbo Diesel engines As these curves show, theinvention produces a steady torque output of approximately 125 ft-lbsfrom 1600 RPM to more than 4000 RPM, whereas the torque curves for theother engines drop off significantly below about 1800 RPM and aboveabout 3000 RPM, never reaching the level of the invention Below 1800RPM, the Diesel engine produces less than about 95 ft-lbs, and the Ottoand Turbo Diesel engines produce less than about 115 ft-lbs Between 3000and 4000 RPM, the outputs of the Otto and Turbo Diesel engines dropbelow 100 ft-lbs, and the output of the Diesel engine drops to wellbelow 80 ft-lbs Thus, the engine of the invention has a higher, broader,and substantially flatter torque output than the Otto, Diesel and TurboDiesel engines, and may be able to use a smaller, lighter and lessexpensive transmission than the other engines.

Curves 77 b, 78 b, 79 b, and 80 b represent the calculated horsepowerproduced by the engine of the invention, the Otto engine, the Dieselengine, and the Turbo Diesel engine, respectively As these curves show,the invention produces significantly greater horsepower than the otherengines, particularly at higher RPM Thus, at 1600 RPM, the inventionproduces about 38 HP, the Turbo Diesel engine produces about 34 HP, theOtto engine produces about 32 HP, and the Diesel engine produces onlyabout 25 HP At 4000 RPM, the invention produces almost 95 HP, the TurboDiesel engine produces about 75 HP, the Otto engine produces about 70HP, and the Diesel engine produces less than 60 HP.

Curves 77 c, 78 c, 79 c, and 80 c represent the calculated fuelefficiency of the engine of the invention, the Otto engine, the Dieselengine, and the Turbo Diesel This unit of measure is used rather thanthe more common miles per gallon in order to provide a more even basisfor comparison since Diesel fuel is heavier and contains more energy pergallon than gasoline Fuel efficiency was calculated as the product of aconstant, horsepower and time divided by the number of pounds of fuelconsumed Although the engine of the invention can run on either gasolineor Diesel fuel, the calculations were based upon the use of gasoline init and in the Otto engine and Diesel fuel in the Diesel and Turbo Dieselengines As these curves show, the engine of the invention produces about45 HP-hours per pound throughout its operating range, whereas the otherthree engines produce no more than about 35 HP-hours per pound and falloff at higher RPM Thus, the engine of the invention uses approximately30 percent less fuel to do the same work as the other engines, whichmeans that the operating expense of the engine will be significantlyless than that of the other engines.

As illustrated in FIGS. 9-11, the pistons can be configured to reducethe volumes of the cylinders when the pistons are at top dead center andthereby increase the compression ratio of the engine This may provide asignificant advantage over conventional engines with poppet valves whichopen into the cylinders and limit the upward travel of the pistons.

In the embodiment of FIG. 9, rotary valves 81 protrude into the upperportion of cylinder 82, and semicylindrical recesses 83 are formed inthe upper portion of piston 84 to receive the protruding portions of thevalves when the piston is in the top center position This permits thepiston to travel almost to the top of the cylinder, reducing the volumeof the cylinder almost to zero and thereby increasing power output andimproving the efficiency of the engine.

In the embodiment of FIG. 10, the rotary valves 81 are recessed in ports86 in cylinder head 87, and piston 88 is formed with projections 89which extend into the lower portions of the ports The projections haveconcave upper surfaces 91 which mate with the curvature of the valves tominimize the volume above the piston in the top dead center position

The piston 92 shown in FIG. 11 is similar to piston 88 with protrusions93 which extend into the lower portions of the ports However, piston 92differs from piston 88 in that the upper surfaces 94 of piston 92 areslightly rounded or convex in order to avoid any possibility of a gaslock occurring between the piston and the valves Alternatively, theupper surfaces of the projections can be made flat or even concave aslong as the curvatures of the protrusions and the valves do not match soclosely that gases can become trapped between the piston and the valves.

The engine can operate with leaner fuel mixtures than other engines,which provides a significant increase in fuel efficiency It is able todo so because there is no burning of the fuel in the compression andexpansion cylinders and, therefore, no chance of burning holes in thosepistons as can happen with lean burning in other engines In a typicalembodiment with the segmented combustion chamber, as little as 10percent of the air going through the chamber needs to support combustionAfter burning, the lean mixture is mixed with the other 90 percent ofthe air, and the gas leaving the combustion chamber has an averagetemperature that is equivalent to having a burn that was 10 times leanerThe lean burn works well in this engine and is useful for low load, lowRPM conditions such as idling Running lean also generates more heat perunit of fuel and, thus, provides higher efficiency.

In other embodiments, as much as 100% or as little as about 3% of theair passing through the combustion chamber may be used to supportcombustion At full power, all the air is used to support combustion, andfuel is injected into all of the segments of the combustion chamber Thatdoes not, however, mean that all of the oxygen is used because theengine runs lean and the burn temperature is held down, e.g. to about1700° K, in order to prevent pollution At very low idle speeds, aslittle as about 3% of the air may be required to maintain the desiredidle speed and to keep the burn temperature at a high enough level, e.g.above 1400° K, to prevent the production of CO.

The engine can also take in large quantities of air at high RPM This canprovide a significant advantage over engines in which the time availableto get a full charge of air decreases proportionately at higher enginespeeds With less air in the cylinder at bottom dead center in a standardengine, not only is there less air available to burn fuel, but theeffective compression ratio is also reduced, and that reduces theefficiency and the total work output of the engine The increased airinput at higher RPM is possible with the engine of the invention becausethe engine normally does not use all of the air that is available Theintake valve normally closes before the compression piston reachesbottom dead center in order to limit the amount of air taken in and thusprovide the correct amount of gas to the expansion cylinder after it isheated and expanded in the combustion chamber By keeping the intakevalve open longer, the engine can provide additional air intake athigher RPM while keeping the compression ratio and efficiency constantWith the efficiency remaining constant, the horsepower produced by theengine continues to increase with increased RPM.

With all of the burning taking place away from the pistons, there is nopossibility of the pistons outrunning a flame front regardless of thespeed of the engine Moreover, there are no slow acting springs in thevalve system, and there is no valve float to compromise compression orcause parasitic pressure losses that waste engine power Full burning ofthe fuel supplied not only gives the engine high efficiency at highengine speeds, but also ensures that all of the energy of the fuel goesinto supplying additional horsepower at high RPM, which is not the casein other engines.

Valve timing and efficiency can be changed by software, and the enginecan trade efficiency for additional horsepower when needed Highefficiency is obtained, inter alia, by exhausting at or near atmosphericpressure and by controlling the valves accordingly If additional poweris desired, then the intake valve can be timed to let in more air whichcan burn more fuel The tradeoff between efficiency and power isespecially useful for short periods of time, such as when accelerating avehicle onto a freeway This temporary loss of efficiency may actuallyresult in an overall improvement in efficiency if the availability ofreserve power permits a smaller, lighter and less expensive engine to beused.

In the disclosed embodiments, the engine works by varying thetemperature or heat of the gas in the combustion chamber Running leangenerates more heat per unit of fuel and thus provides higher efficiencyEngines in which combustion occurs in cylinders with pistons are limitedin their ability to use leaner mixtures because of the possibility ofthe leaner mixture burning holes in the pistons

The engine also has unusually low heat loss, which further improvesefficiency Pressurized gas can be expanded to its useable limit nearatmospheric pressure Discharging the exhaust gases at atmosphericpressure reduces the temperature of the exhaust and, hence, the amountof heat which is lost with them. Moreover, the head of the engine can berelatively small, with relatively little surface area to lose heat tothe ambient air Also, in an engine which does not require water coolingof the head, there is less heat loss than in engines which are cooled.

The engine produces substantially no NO_(X), unburned hydrocarbons orcarbon monoxide, and emits only minimal particulate matter, smoke andsoot, and it does so without additional components such as catalyticconverters and particle filters.

In conventional gas and Diesel engines, NO_(X) is produced when theflame temperature exceeds 1800° K, and it is commonly reduced bymonitoring the exhaust and redirecting the exhaust back to the airintake if it is rich in oxygen With Diesel engines, some form of aftertreatment with a reducing agent such as urea may be required.

In the engine of the invention, the temperature in the combustionchamber is monitored and controlled to limit the maximum burntemperature to 1700° K, which is well below the range where NO_(X) isformed Also, the engine does not have widely varying temperature swingslike other engines may have, and it has a much more constant temperatureat any particular power setting, which makes temperature control mucheasier to maintain

Unburned hydrocarbons may occur in some engines because the time thefuel remains in the cylinders is too short for complete combustion, andsome of the fuel is left in the cylinders without being burned In atypical engine running at 3,000 RPM, for example, the fuel must bemixed, ignited and burned and exhaust must start in only 1/100 of asecond In addition, the water cooled cylinders in such engines can becold enough to quench the flame front of the burning fuel, which canfurther prevent all of the fuel from burning The unburned fuel condenseson the cylinder walls and is then blown out with the exhaust.

The engine of the invention does not produce significant amounts ofunburned hydrocarbons The burning takes place in a thermally insulatedcombustion chamber which has hot walls that do not quench the flamefront and do not cause condensation of the fuel The combustion chamberoperates at high pressure and has a much larger volume than a standardengine As a result, the gases remain in the combustion much longer(typically 2 to 25 times) than they do in the cylinders of conventionalengines, and thus there is more time to complete the burn so that thereare no unburned hydrocarbons In addition, the combustion chamberproduces turbulence which causes more complete mixing and furtherreduces the chance of having any unburned hydrocarbons The sharpprotrusions that form hot spots in the combustion chamber also createturbulence and help to ensure complete combustion and prevent unburnedhydrocarbons from leaving the combustion chamber as pollutants.

Carbon monoxide (CO) is produced in other engines when there is notenough time for complete combustion of the fuel, and/or when the flametemperature is too low for oxygen in the air to combine with CO toproduce harmless carbon dioxide (CO₂), and/or when there is not enoughoxygen to combine with the CO to make CO₂.

As discussed above, with the engine of the invention, the fuel remainsin the combustion chamber much longer than it does in conventionalengines CO emissions are significantly reduced or eliminated, becausethere is much more time to complete the burn process In addition, theburn temperature is monitored and controlled by adjusting the amount offuel delivered to the combustion chamber With the combustion chambersegmented so that only a fraction of the total airflow is mixed with thefuel and burned, temperature within the individual segments of thechamber can be controlled to provide a burn temperature between 1400° Kand 1700° K, which is hot enough to ensure that all of the burn productsare oxidized and cool enough to prevent the formation of NO_(X) Thenumber and size of the combustion sections which are injected with fuelcan be chosen to maintain good control of both the burn temperature andthe power level of the engine CO production is further prevented byrunning the engine with leaner fuel mixtures than are possible in otherengines The leaner mixtures have an abundance of oxygen which cancombine with CO to convert it to CO₂ With the abundance of oxygen and byoperating at the correct temperature for extended periods of time, theengine can avoid producing measurable amounts of CO.

Soot and other particulate matter are typically produced by the highpressures that are present in very high compression ratio engines byinjecting fuel into air that is too hot and by burning rich fuelmixtures With the engine of the invention, however, the long residencetime of the fuel in the combustion chamber is effective in burning upparticulate matter and soot and thereby converting it from a carbon richmaterial to water vapor and CO₂ In addition, in some embodiments, theengine operates most efficiently with compression ratios between 10:1and 15:1 where the potential for making soot is substantially less thanin Diesel engines which operate at significantly higher compressionratios Soot production is further reduced by maintaining the temperatureof the air at the point of injection below the temperature at which sootis produced Thus, for example, with the engine having a compressionratio of 13:1, the temperature of the compressed air is about 850° K,which is below the critical fuel injection temperature for sootproduction (900° K) and also well below the injection temperatures ofDiesel engines which are typically about 1200° K Also, with the leanfuel mixtures on which the engine can operate, there is an abundance ofoxygen to complete the burning process and convert all of the soot intowater vapor and harmless carbon dioxide.

The invention has a number of important features and advantages Withwidely variable valve timing, complete burning of fuel at all enginespeeds and loads, and the ability to vary the amount of air intake andexhaust pressures without doing any net work against the atmosphere, theinvention provides a highly flexible engine which can operate with highefficiency at substantially all engine speeds and load conditions

By separating the compression, combustion, and expansion phases of thecycle, better control of each is obtained, and efficiency is improved byexhausting the spent gases from the expansion cylinder at or nearatmospheric pressure, where the energy remaining in them due to pressureis negligible This results in a significant improvement over otherengines where as much as 30 percent of the total engine power is wastedthrough the exhaust As the pressure of the exhaust gases is reduced, sois the temperature of the gas being expanded, and lower exhausttemperatures also provide higher engine efficiency.

With the variable valves, the compression ratio of the compression andthe expansion ratio of the expansion cylinders can be adjusted bycontrolling the amount of air taken into the compression cylinders andthe amount of gas delivered to the expansion cylinders In addition, theexpansion ratio can be made higher than the compression ratio, which isnot possible in other engines.

The invention also avoids the loss of power and efficiency which occursin other engines when the pressure in the cylinders drops belowatmospheric pressure and the engine must do work against the atmosphericpressure on the under sides of the pistons By controlling the valvetiming so that no valve in the compressor or expander is opened on theupstroke of a piston until the pressure in the cylinder is no longersubatmospheric, the work done against atmospheric pressure is stored andthen recaptured so the net effect on the efficiency of the engine forhaving done work against atmospheric pressure is essentially zero.

With no valves extending into the cylinders, the volumes of both thecompression cylinders and the expansion cylinders can go almost to zerowhen the pistons are at their top dead center positions, and volumetricefficiency is, thus, maximized which further adds to fuel efficiency.

Moreover, the engine of the invention does not have the problem ofdecreased efficiency which other engines may experience when the amountof air admitted on the intake stroke is reduced at power levels lessthan full power The problem arises in other engines because reducing theair intake causes the pressure in the cylinder to drop below atmosphericpressure during the downward stroke of the piston This reduced amount ofair reduces the effective compression ratio of the engine and causes thepiston to do lost work against the atmospheric pressure on the undersideof the piston The engine of the invention, however, does not have thatproblem because the top dead center pressure of the compression cylinderis determined by when the outlet valve opens to admit the compressed airto the combustion chamber and when the inlet valve closes Since thevolume of the compression cylinder goes almost to zero, the compressionpressure can be set to almost any desired level regardless of how muchair was admitted to the cylinder Thus, constant efficiency can beprovided at varied air intake levels.

Another advantage of the invention is that the engine can run with asubstantially constant compression ratio under substantially all loadconditions, whereas in other engines the compression ratio can vary withload by as much as a factor of 3 Since the efficiency of an internalcombustion engine is proportional to the compression ratio (at least forratios up to about 20:1), with the substantially constant compressionratio, the efficiency of the engine remains high throughout its range ofoperation.

Moreover, with the compression ratio substantially constant and theexhaust pressure effectively equal to atmospheric pressure at all loadsand speeds, the torque of the engine is also substantially constant forall loads and engine speeds Furthermore, with combustion not takingplace in a cooled chamber with moving pistons, the engine does not havelimitations on speed and torque that other engines typically have Thereis no piston to outrun the flame front and no possibility of valve floatThis allows the engine to run very efficiently at all speeds and loads.

The flat torque curve has another advantage in that it allows the engineto be used with a transmission which has fewer gears and is thereforesmaller, less expensive, and lighter in weight than the transmissionsrequired by other engines This reduction in weight further increasesfuel efficiency.

Since the fuel is fully burned in a separate combustion chamber, fullpower is applied to the expansion pistons when they are at top deadcenter Therefore, the expanding gases push on the pistons for more oftheir stroke than in other engines where the flame front moves slowlyand does not produce maximum pressure until the flame front reaches thecylinder walls and the pistons have moved well past top dead center,e.g. 45 degrees past top dead center in an engine running at 3,000 RPMThus, with the engine of the invention, the maximum pressure isavailable longer and the total work output is greater for a given amountof hot gas This also results in higher fuel efficiency than is possiblein other engines.

The engine provides a significant improvement in fuel efficiency, andwith closed loop pressure and temperature controls and no combustion inthe cylinders with moving pistons, it produces substantially no NO_(X),unburned hydrocarbons or carbon monoxide, and emits minimal particulatematter such as smoke or soot Since the engine runs so cleanly andquietly, in many applications it may not require either a catalyticconverter or a muffler The engine can run on different fuels, and canmake necessary adjustments automatically as different fuels aresupplied.

In some embodiments, the engine provides variable engine braking as wellas very efficient and effective compression release engine braking whichis also much quieter than such braking with conventional Diesel enginesUnlike other internal combustion engines, the engine of the invention iscapable of operating at high efficiency even at partial loads The engineis easy to start and does not need a dedicated starting motor Itrequires no spark plugs or ignition system, and maintenance requirementsare low.

The ratio of compression cylinders to expansion cylinders is not fixed,and the cylinders can also have similar or different bores and/orstrokes For example, a 4-cylinder engine may have two compressioncylinders and two expansion cylinders A 6-cylinder engine may have twocompression cylinders and four expansion cylinders or an equal number ofeach Similarly, different embodiments of the engine can have differentnumbers of combustion chambers.

Moreover, with the invention, the horsepower of a given engine can begreatly increased for a short period of time without appreciablyaffecting the overall efficiency of the engine Thus, by sacrificingefficiency for a just few seconds at a time, horsepower can be increasedby 50% or more, when needed, such as when accelerating a vehicle onto afreeway.

It is apparent from the foregoing that a new and improved internalcombustion engine and method have been provided While only certainpresently preferred embodiments have been described in detail, as willbe apparent to those familiar with the art, certain changes andmodifications can be made without departing from the scope of theinvention as defined by the following claims.

1. An internal combustion engine having compression and expansioncylinders, an intake valve for controlling air flow to the compressioncylinder, an outlet valve for controlling flow from the compressioncylinder, an inlet valve for controlling flow to the expansion cylinder,an exhaust valve for controlling flow from the expansion cylinder, andmeans for varying the compression ratio of the engine by varying thetiming of the inlet and outlet valves.
 2. The engine of claim 1including means for delaying opening of the intake valve until pressurein the compression cylinder is at or near atmospheric pressure.
 3. Theengine of claim 1 including means for opening the exhaust valve whenpressure in the expansion chamber is at or near atmospheric pressureduring normal operation of the engine.
 4. The engine of claim 1including means for opening the exhaust valve when pressure in thecombustion chamber is at or near atmospheric pressure during normaloperation of the engine.
 5. The engine of claim 1 including means formaintaining a substantially constant pressure in the combustion chamberduring normal operation of the engine.
 6. The engine of claim 1including means for increasing airflow through the engine when theengine is operating at high altitude, high ambient temperatures, and/orhigh RPM, and/or when engine breathing is otherwise limited.
 7. Aninternal combustion engine, comprising: a compression cylinder, acylinder head at the top of the compression cylinder, a piston in thecompression cylinder, a crankshaft constraining the piston forreciprocating movement in the compression cylinder between a top deadcenter position in which the piston is less than 0.150 inch from thecylinder head and a bottom dead center position, a combustion chamber,an outlet valve for controlling communication between the compressioncylinder and the combustion chamber without interfering with themovement of the piston to the top dead center position, and a fuel inletfor introducing fuel into the combustion chamber for combustion with airfrom the compression cylinder.
 8. The engine of claim 7 wherein theoutlet valve is a rotary valve which does not project into thecompression cylinder.
 9. The engine of claim 7 wherein the compressioncylinder has a compression ratio in the range of about 10:1 to 18:1. 10.The engine of claim 7 wherein the piston is less than 0.015 inch fromthe cylinder head in the top dead center position.
 11. The engine ofclaim 7 wherein the outlet valve is a rotary valve, and the piston inthe compression cylinder has a contoured surface which interfits withthe valve to minimize the volume of the compression cylinder when thepiston is at top dead center.
 12. The engine of claim 7 including meansfor maintaining a substantially constant pressure in the combustionchamber during normal operation of the engine.
 13. The engine of claim 7including means for increasing airflow through the engine when theengine is operating at high altitude, high ambient temperatures, and/orhigh RPM, and/or when engine breathing is otherwise limited.
 14. Aninternal combustion engine, comprising: a compression cylinder, a pistonin the compression cylinder, a crankshaft constraining the piston forreciprocating movement between top and bottom dead center positions inthe cylinder, a combustion chamber, an outlet valve for controllingcommunication between the compression cylinder and the combustionchamber, and a fuel inlet for introducing fuel into the combustionchamber for combustion, wherein the compression cylinder has a strokelength and a compression ratio, and the outlet valve is configured toallow air to flow from the compression cylinder to the combustionchamber during the upstroke of the piston such that the clearancebetween the piston and the head of the compression cylinder at top deadcenter is less than the sum of the stroke length and the clearancedivided by the compression ratio.
 15. The engine of claim 14 wherein nocombustion occurs within the compression cylinder.
 16. The engine ofclaim 14 wherein the outlet valve is a rotary valve, and the piston inthe compression cylinder has a contoured surface which interfits withthe valve to minimize the volume of the compression cylinder when thepiston is at top dead center.
 17. The engine of claim 14 including meansfor maintaining a substantially constant pressure in the combustionchamber during normal operation of the engine.
 18. The engine of claim14 including means for increasing air flow through the engine when theengine is operating at high altitude, high ambient temperatures, and/orhigh RPM, and/or when engine breathing is otherwise limited.
 19. Aninternal combustion engine, comprising: a compression cylinder, acylinder head at the top of the compression cylinder, a piston in thecompression cylinder, a crankshaft constraining the piston forreciprocating movement between top and bottom dead center positions inthe compression cylinder, an intake valve through which air is drawninto the compression cylinder, a combustion chamber, an outlet valvewhich opens to admit air from the compression cylinder to the combustionchamber while the piston is moving toward the top dead center position,a compression ratio defined as the volume of air drawn into thecompression cylinder divided by the volume above the piston in thecombustion cylinder when the outlet valve opens, with the pistoncontinuing to move toward top dead center position after the outletvalve opens and the distance between the piston and the cylinder headwhen the piston is in the top dead center position not being limited bythe compression ratio, and a fuel inlet for introducing fuel into thecombustion chamber for combustion with air from the compressioncylinder.
 20. The engine of claim 19 including means for maintaining asubstantially constant pressure in the combustion chamber during normaloperation of the engine.
 21. The engine of claim 19 including means forincreasing air flow through the engine when the engine is operating athigh altitude, high ambient temperatures, and/or high RPM, and/or whenengine breathing is otherwise limited.